Draft tube for hydraulic turbines



June 30, 1925. 1,544,485

J. D. SCOVILLE DRAFT TUBE FOR HYDRAULIC TURBINES Filed Deo. v'. 1923 l s srvxees-shee'c 1 c fj; 9' ,1.

Inge-nto:

attentat June 30, 1925. 1,544,485

J. D. SCOVILLE:

l`DRAFT TUBE Fon HYDRAULIC TURBINES Filed Deo. v. v1925 3 sneetssheet g .1.15. scovlLLE DRAFT TUBE FOR HYDRAULIC TURBINES June 30, 1925.

Filed Deo. '7. 1923 3 Sheec,s-Sheet 5 Patented y June 30, 1.925.

UNITED STATES PATENT OFFICE.

JAMES D. SCOVILLE, OF YORK, PENNSYLVANIA, ASSIGNOR TO S. MORGAN SMITH OO.,

OF YORK, PENNSYLVANIA, A CORPORATION 0F PENNSYLVANIA.

DRAFT TUBE FOR HYDRAULIC TURBINIS.

Application filed December 7, 1923. Serial No. 679,144.

To all whom t may concern:

Be it known that I, JAMES D. SooviLLE, a citizen of the United States, residing at York, in the' county of York and State of Pennsylvania, have invented new and useful Improvements in Draft Tubes for Hydraulic Turbines, of which the following is a specification.

This invention relates to draft tubes for either vertically or horizontally disposed hydraulic turbines. The improved draft tube is of the angular elbow type, comprising a primal tube member disposed to receive the water direct from a vertically or horizontally arranged turbine runner and opening into an angular vmember discharging or liberating the water into a tail race or analogous means for carrying the water away from the complete draft tube'comprising the two members.

In the vertical shaft type of turbine the water is discharged from the runner vertically downward and must be turned tov a horizontal direction during passage to the tail race. The water leaves the runner at a relatively high'velocity, and'inasmuch as this represents a considerable amount of energy, the velocity must be gradually decreased and discharged from the draft tube at a relatively low velocity, thus regaining as much as possible of the said energy of the water as it leaves the runner. Since the height that the runner may be placed above tail water is limited by the atmospheric pressure. or by the seal over the turbine required in low head installations and by the depth under tail water, because of the high cost of deep pits, it is desirable to turn the water from a vertical to a horizontal direction in a short space, and at the same time reduce the velocity to a low value.

Tests have shown that the best draft tube for all purposes is the vertical, conical type with an angular flare of about four to six degrees with a considerable depth under .the

mouth, to allow the water to be discharged from the draft tube without back pressure, disturbance or other avoidable losses. This type of tube must be relatively long to reduce the velocity to a low value, and inasmuch as the height which .the runner may beset above tail water is limited as described above, it follows that the vertical, conical' tube requires a comparatively deep pit, ex-

into the tail race.

cept for very small turbines, and for large turbines the length of the vertical tube and depth of the pitv necessary to reduce the velocity lof the discharge to the usual amount becomes so great as to make the cost prohibitive. Other types of draft tubes have been designed to reduce the required depth of excavation, but they have been objectionable because they embody shapes and sections diflicult and expensive to form in either concrete or metal, and usuall require excessive width, thus lengthening t e power house and making it diiicult to provide proper foundational support for the power house. These tubes, therefore, add greatly' to the cost of installation.

The usual form of elbow draft tube is not objectionable because of depth and width'of excavation, or difficult and expensive foundational support, but because it is diicult and expensive to form in either concrete or meta-l, and it does not regaln the energy of discharge of the water as it leaves the/runner as completely as possible.

One of the. objects of the present invention is to eliminate the objections to the ,c

different types of draft tubes above menv tioned and provide a comparatively inexpensive draft tube which does not require a deep or wide pit and does not decrease the eiiiciency of the turbinebelow that obtained with the vertical, conicaltype of tube.

It is also known as the result of experiments that it-,is more efficient to allow the water to descend vertically through a passage with constantly increasin area by maintaining the center line of t e passage vertical to the lowest practicable position to reduce the velocity of the water as much as possible, and then allowing the water to spread out somewhat before passing through the horizontal part of the passage The water in the vertical part of the passage or draft tube descends in such m'anner that in each sector o f equal angular extent there is an approximately equal quantity of water. The velocity at the outside of the passage or tube is usually greater than at the inside, and in` away must be guided to the tail race by the horizontal portion of the draft tube, and this portion of the draft tube is quite important, inasmuch as a considerable amount of energy due to the velocity of the wat-er still remains, which must be regained if the tube is to produce the maximum possible eBiciency. This is done by increasing the area of the passage in a vdown-stream direction. Thus when the water reaches the discharge end of the draft tube it flows slowly and smoothly into the tail race.

It is a further ob 'ect of this invention to provide an elbow draft tube having a primal member to receive the water from the runner with an increased area at the outletportion thereof relatively to the discharge area of the runner, and to make the enlarged extremity of the primal member on a slope at an angle of inclination, so that the water may be efficiently taken care of by the angular elbow guiding passage, the volume of water entering the angular elbow member serving as a guiding passage increasing from the. upstream part of the downstream part of the latter. A still further object of the invention is to utilize the enlarged upwardly sloping or inclining outlet extremity of the primal draft tube member, in cooperation with an angular elbow member serving as a guiding passage having either a level or a sloped bottom.

The disadvantages incident to draft tube constructions as heretofore proposed and practically developed do not aifect the present improved form of tube. The water in the improved form of tube sometimes has a slightly whirlingy discharge from the receiving to the discharge extremity of the primal tube member, or at times a full or more than full revolution of the water may ensue. The sloped or inclined formation of the discharge extremity of the primal draft tube member embodying the present features'of the invention operates to give a freer outlet towards the downstream side of the draft tube than towards the upstream side. This is materially advantageous in all cases, as the water must eventually move in a downstream direction.

It will be understood that it is proposed to use the improved elbow draft tube construction in various applications, and when it is applied to a horizontally disposed turbine, the axis of the primal member extends from the runner in a horizontal direction and the secondary or angular elbow member, which receives the water from the primal member, is substantially vertical in its disposition. The operation of the water discharged `from the primal member of the improved draft tube has the same freedom of movement in a ldownstream direction in either application of the improved tube.

member whichserves as a' Aprimal member to the In the accompanying drawings various embodiments of the improved draft tube construction are illustrated for the purpose of demonstrating the practicability thereof, but it will be understood that such changes and modifications will be at all times adopted without departing from the spirit of the invention or scope of the claims appended hereto.

In the drawings:

Fig. 1 is a vertical section through a vertically disposed turbine and runner vembodying the features of the invention;

Fig. 2 is a view similar to Fig. 1, showing l a slight modification of the structure;

Fig. 3 is a horizontal section taken on the line 3-3, Fig. 2;

Fig. 4 is a view similar to Figs. 1 and 2, showing a further modification of the structure;

Fig. 5 isa horizontal section on the line 5-5, Fig. 4; and

Fig. 6 showing the features of the invention applied to a horizontally disposed turbine.

As shown by Figs. 1, 2 and 4 the numeral 5 designates a vertical type of turbine having an upwardly extending shaft 6, a runner 7 and suitably operated gates 8, which control the inlet of the water to the runner 7 and in practice may be supplied through the medium of a scroll case well known in hydraulic installations. In Fig. 6 the invention is applied to a horizontally disposed turbine installation 9 having a runner 10 with a horizontally extending shaft 11 and gates 12, all operating similar to the Vertical turbine installations as shown by Figs. 1, 2 and-4 and differing from the latter only in a change of position.

In all of the applications of the improved draft tube two essential draft tube members or components are disclosed, namely, a primal draft tube member 14, which receives the water discharged from the runner, and an angularly disposed member 15, which in the'several forms illustrated may be slightly varied and will be hereinafter specifically referred to. In the application of the invention as shown by Fig. 6 the rimal draft tube member or component 16 as its axis extending in a horizontal direction and the angular draft tube member or component 17 is disposed substantially vertical, to accommodate the application of the improvement to a horizontally disposed turbine installation.

In all of the structures illustrated the primal draft tube member or component 14 or 16 has a similar construction in essential features and gradually diverges or increases in diameter from the receptive extremity thereof adjacent to the runner towards the discharge extremity communicating with the angular member or component is a longitudinal vertical section,

IlU

15 or 17, and, furthermore, the enlarged extremity of the primal draft tube member or component 14 in all of the forms shown has its enlarged extremity sloped or inclined upwardly from the upstream longer portion thereof towards the downstream shorter portion, as at 18 to 19. A. slight difference in, structure of the outlet extrem; ity of the primal draft tube member or component 14 is shown by Fig. 4, the variation consisting of a slight curvature or Hare, as at 20, `these flaring curves, which merge into different portions of the upper walls of the angular draft tube member or component into which the said primal member discharges, having radii by which they are defined materially less in lengththan half thel diameter of the enlarged or outlet extremity of the primalvmember or component 14 or 16 of the draft tube.

In the construction of the improved elbow draft tube as shown by Figure 1, the lower enlarged upwardly sloped or inclined discharge extremity of the primal member or component 14 extends into the angular elbow member or component 15 or depends below the top wall of the latter. rlhe angular elbow member 15 as shown by Fig. 1 is in the form of a pit having a substantially horizontal straightor flat bottom 21 and a top walll 22 also substantially horizontal, the lower extremity o f the primal draft tube member or component being located at a distance from the end wall 23 so as to give ample space for discharge. The level of the tail water in this pit is indicated at 24a and the direction of flow or discharge of the water `from the member or component 14 into the member orcomponent 15 is indicated by the arrows 24, 25, and 26, which are pointingl downstream. The upward slope in a downstream direction of the discharge extremity of the member of the draft tubel receiving the water from the lrunner is to give more area in .a downstream direction -and to allow the water to bev more readily discharged ina downstream direction.

In the application of the invention as shown by Fig. 2, the horizontal member or 'component 15 has a lower substantially horizontal straight wall 27 and a top upwardly and outwardly inclined wall 28, and the lower sloped or inclined enlarged extremity of the primal member or component 14 terminates and intersect-s the rear terminall of the top wall 28 and also a short inclined wall 29 adjacent to the vertically reduced terminal or end vwall 30 of the member 15, the short top wall 29 -having the same inclination as the lower enlargedoutlet extremity of thev member or component 14. The distance lof the short vertical end wall 30 from the lowermost maximum depending portion of the draft tube member or component 14 permits a relief or/a freer discharge. of the water from the member or component 14 into the member 15 at this point, the water taking the course as indicated by the arrows in Fig. 3 in a downstream direction.

In the modification shown by Fig. 4 the bottom' 31 of the angular elbow member or component 15 is inclined downwardly, the top wall 32 being similar to the wall 28 as shown by Fig. 2, and moreover, the rear short top wall 33 is like the rear wall 29 as shown by Fig. 2. The feature of difference as hereinbefore referred to in this modified structure is the curved flared construction, as at 20, of the discharge or outlet end of the member or component 14, the lower terminal of the curved are merging into the respective walls 32 and 33.l The rear end 'wall 34 of the member or component 15 as shown by Fig. 4 is also vertical' as in the form shown by Fig. 2. rllhe bottom inclined wall 31 assists in the downstream flow of the water through the member or component l5 towards the tail race or other means for carrying the water away from the improved draft tube structure.` The course of the water in the component 15 as shown by Fig. 4 is clearly' illustrated in Fig. 5 from the rear end wall in a downstream direction by the arrows.

The angular elbow members or components 15 as shown by Fig. 2 are restricted pit structures whichl cooperate with the primal draft tube member or component, and the main object in view in both the substantially horizontal or level bottom structures 27 of Fig. 2 and the downwardly sloped or inclined bottom 31 of Fig. 4 is to save excavation, particularly in the case of turbine installations which will not admit of a very deep pit structure. It will also be seen in F igs; 3and 5 as illust-rated by dotted lines that the side walls 35 and 36 of the angular elbow members or components of the restricted pit typey are outwardly converged, so as to give further deceleration of the water passing from the angular members' or components 15 into the tail race or other medium of conveyance for the water. It will further be seen that the level of the tail water in both forms of the improved: draft tube as shown by Figs. 2 and 4 stands above the uppermost wall of the members or components 15 in these two forms 4as at 37. Also, in Figs. 2 and 3 the same direction of flow from the primal member or component 14 into the angular member or component15 and through the latter is indicated by arrows similar to those shown ,by Fig. 1. In the application of the improved draft tube to a horizontally arranged turbine as shown by Fig. 6, the structure is in all respects similar to that illustrated by Fig. 2, with the exception that the bottom wall of the member or component shown by Fig.

2 is arranged as the outer vertical wall 38' of the component 17, and the upper portion 89 of the inner side wall corresponds to the short top wall 29 in Fig. 2, and the lower portion of the inner wall in Fig. 6 corresponds to the outer longer inclined top wall 28 illustrated by Fig. 2.. The arrows 41, 42 and L13 also indicate in. Fig. 6 the same direction of fiow of the water from the. mem ber or component 16 into and through the angular member or component 17 i In this ronnection it will be understood that the same structure as shown by Fig. 6 may be used with a pair of horizontal shaft turbmes, the change only requiring a duplication of parts.

As hereinbefore indicated, the water passing through the primal member or component 14 or 16 is discharged into the angu lar member or component 15 or 17 with` freer movement, in view of the difference of length of the primal member or component 14 or 16 on opposite sides of the central axis thereof and regularly therearound, and also the several forms of the angular members or components 15 and 17 have their rear walls at a distance from the/maximum extent of the primal member or component from the runner, so as to/permit the-water to freely discharge in opposite directions to the sides of the angular members or components y 15 and 17 to reduce the formation of eddies and confusion of the water discharged at this part of the improved draft tube structure. vTo save excavation and reduce cost of construction and yalso facilitate flow of the water downstream through the member or component 15 or 17, it is intended, as shown by Fig. 5,*to eliminate the corners or angles between the side and rear walls as shown by Fig. 3 and construct these intersecting portions of the walls in curved lines or as fillets, as at 44. l

In addition to the advantages of the slope or inclination of the enlarged outlet extremity of the main tube or chamber and Whereby the water is facilitated in its discharge in a downstream direction, the water which may be whirling as it passes through and is discharged from the member 14 is allowed to continue its whirling movement in the elbow or angular member 15 or 17 and along the latter to the outlet thereof, or in the same plane as the said angular or elbow member 15 or 17. The sloped or inclined bottom wall 31 of the angular or elbow member 15 should not be at too great an angle, to avoid any tendency to produce confusion of the-water at the back of the. tube member 14.

From the foregoing description it should be understood that the improved elbow draft tube has been devised and practicallyoperates to overcome deciencies in draft tube constructions heretofore usedl and in which water may be turned froma vertical to a horizontal flow or from a horizontal to a vertical flow in connection with a horizontally disposed Jturbine. The essential feature of the invention irrespective of the construction of the secondary or angular draft tube member in the several forms hereinbefore described is the main draft tube member which receives the water directly fromI the runner or other water-driven device of a turbine having an increased area at the outlet extremity thereof relatively to the discharge area of the runner, and to make the said enlarged discharge extremity on a slope or at an angle of inclination in a downstream direction relatively to the secondary or angularly disposed elbow member, in order to give a freer outflow from the said main or primal waterreceiving element or member, and it should be further understood that it is not intended that the invention be .limited to the exact angle or inclination shown, or the particular devisement hereinbefore explained and. embodying a slope or angle of inclination, as it is proposed to utilize any other structure that will shorten the length of the main or receiving member of the draft tube in direct communication with the runner or other water operated means of the turbine at one side of the axis of the said latter member, and to dispose the shorter extent of this main member of the draft tube so that it will discharge towards the downstream direction of movement of the water in the remaining portion or member of the draft tube, with material advantages in elciency of operation of the turbine.

Vhat is claimed as new is:

1. An elbow draft tube comprising primal tube member to receive the water from a turbine, and an angular member, the primal member being diverged and decreasing in length towards its discharge extremity in the downstream direction of the angular member.

2. An elbow draft tube comprising a primal memberf'fand an elbow member at an angle thereto, the primal member being diverged at its outlet extremity and gradually shortened in length from the upstream towards the downstream direction of the angular elbow member. l

3. An elbow draft tube comprising a primal member to receive the water directly fromv a turbine, and an angular elbow member, the primal member having a diverged outlet extremity with an upward terminal slope, the outlet extremity of the primal member being freely open to the angular elbow member. l

L1. A water-receiving draft tube member having a discharge extremity with a forward upwardly inclined terminal.

Y 5. A water-receiving draft tube member of van elbow draft tube regularly diverging van elbow draft tube of and decreasing in length from a maximum to a minimum extent at the forward downstream portion of the discharge extremity to accelerate the discharge of the water from the member.

6. A water-receiving tubular member of gradually diverging fully at its outlet extremity and decreasing in length in advance of the longitudinal axis and at the downstream side portion of the member, and means at an angle to the said member and into which the latter discharges. f

7. In an elbow draft tube, a primal member forreceiving water'from a turbine gradually increasing in diameter towards its outlet extremity, the outlet extremity being inclined to gradually reduce the length of the member towards one side of the longitudinal axis at the downstream' side porposed at an angle of inclination, and an tion of the member, and means into which the member discharges.

8. An elbow draft tube `comprising a primal member gradually increasing in diameter fully to its discharge extremity to receive water from a turbine, the discharge extremity of said member being also disangular elbow member into which the primal member discharges, the incline of tion the dischargel extremity of the primal mem-v ber being from a lowermost point at the up-stream portion of the angular elbow member upwardly to theV highest point in the direction of the downstream portion of the said angular member. j Y

9. In an elbow draft tube, a primal water-receiving t-ubular member havingv a discharge extremity which .is inclined and enlarged and an angular elbow member with which the discharge extremity of the primal member has communication, the angular elbow member lhaving a divergence relatively to the discharge extremity of the said primal member. v

10. An elbow draft tbe comprising a primal tubular memberto receive water from a turbine, the said member having an enlar ed extremity with an upward inclinaom a maximum to a minimum'extent thereof, and an angular'elbow member with which-the, discharge extremity of the primal member has open communication, the an lar elbow 'member having a downwar ly sloping bottom in the direction of the down-l stream course thereof.

lai-ly intersecting members, the one member having an enlarged upwardly sloping forlig'ard portion opening into the other mem- 12. An elbow draft tube consisting 'of a vertically disposed primal member to receive `water from a turbine, the said mem- 11. An elbow draft tube comprising angu ber'gradually diverging downwardly and' having an upwardly slopedbottom, and an elbow member atan angle to the said vertical member, the vertical member having its greatest dependence at the upstream portion of the said angular elbow member.

13. An elbow draft tube consisting of a vertically disposed primal member to receive water from a turbine, the said member gradually `diverging downwardly and having an upwardly sloped bottom, and an elbow memberv at an angle to the said vertical member, the vertical member .having its greatest dependence at the upstream portion of the said angular elbow memberv and located at a distance from the upstream end wall of the said angular elbow member.

14. Thel combination with a turbine having water operated means, of an elbow draft tube comprising a primal tube member diverging from the turbine and having its discharge extremity sloped at an upwardV angle of inclination from a maximum to a minimum extending portion thereof, and an angular elbow member with which the en larged sloped discharge extremity of the prim'almember has communication.

15. An elbow draft tube comprising a primal member to receive the water directly from a turbine and anangular elbow member, the primalmember having a diverged outlet extremity, with an upwardterminal slope, the outlet extremity having a curved iared construction merging into the angular elbow member.

16. An elbow draft tube comprising a primal member to receive water directly from a turbine and an angular elbow member, the primal member having a diverged outlet extremity with an upward terminal slope, and the angular elbow member also diverging in a downstream direction.

In testimony whereof I have hereunto'set my hand. v

1 JALIES D. SCOVILLE. 

